1. Instructor: Craig Duckett cduckett@cascadia.edu
Introduction to Programming
Instructor: Craig Duckett
Counters and Counting Loops

2. Today’s Topic: Counters and Counting Loops
Review: if and while Statements
Boolean conditions (true or false)
Example code of both statements in action
Counters
What Good are They?
How are They Used?
Example code of counter in action

3. REVIEW: if and while Statements
Both the if and while statements evaluate Boolean conditions
They test to determine whether a condition is true or false
True, do something
False, don’t do something
Do it!
Don’t
do it!

4. CONCEPT: The if Statement
IF EXAMPLE: Taking a free right-turn at a red light
“If it is clear (no vehicle or pedestrian coming),
then take a free right turn.”
Do This
The Next Thing
The Next Thing

5. The if Statement “If true, do it once …”
False

6. if Example Code
WALK-THROUGH: RobotWall.java

7. CONCEPT: The while Statement (Loop)
WHILE EXAMPLE: Buying Gum Balls
“While I have enough quarters, buy a gum ball; keep buying gum balls as long as I have enough quarters.”
Do This
The Next Thing
The Next Thing

8. The while Statement “While true do it again…”
False

9. while Example Code
WALK-THROUGH: RobotWall.java

10. If and While
When the simplest form of an if statement asks a question and the answer is true, it executes a group of statements once and then continues with the rest of the program. If the answer to the question is false, that group of statements is not executed.
When a while statement asks a question and the answer is true, it executes a group of statements (just like the if statement). However, instead of continuing down to the rest of the program, the while statement asks the question again. If the answer is still true, that same group of statements is executed again. This continues until the answer to the question is false.
The if statement’s question is “Should I execute these statements at least once?”
if (test condition) {
// Statements of things to do }
The while statement’s question is “Should I execute these statements again?”
while (test condition)

13. QUESTION
With the while loop, what would happen if the condition was always true?

14. ANSWER
An infinite loop!

15. while Example Code
WALK-THROUGH: RobotWall.java

16. QUESTION
Is there a way to configure a set number of times to go through the loop, and then stop or jump out to prevent an infinite loop?

17. Yes! You can do this by setting up and using a counter!
ANSWER
Yes! You can do this by setting up and using a counter!
I’m a
counter.
pretty big
deal!

18. What is a Counter ?
A counter is a variable, usually of an integer int data type, typically initialized to start with a 0.
A variable is a small section of memory that has been set aside based on the size and type of data it will contain.
It is given a unique name and then an initial starter value.
As the program is run this value can be changed, it can vary, hence the name variable.

19. Setting Up a Counter
In the code, setting up a counter for use with a loop is a 3-Step Process:
Create and initialize the counter
Create the count condition
“Increment” the counter by 1
Let’s take a look at what this means and how it works with our while loop program…

20. Counter Example Code WALK-THROUGH: RobotWall.java
int counter = 0; // (1) Create the counter
while(counter < 5) // (2) Create the count condition { lisa.putThing(); lisa.move(); counter = counter + 1; // (3) Increment the counter by }
WALK-THROUGH: RobotWall.java

21. Counter Increment/Decrement
int counter = 0; while(counter < 5) { lisa.move(); counter = counter + 1; }
int counter = 5; while(counter > 0) { lisa.move(); counter = counter - 1; }

22. In-Class Exercises
From the menu bar, select Lectures and go to the Lectures ## bar and select ICE 5, then ICE 6 to begin working on today's in-class exercises.